Israel begins the 34th General Assembly of the United Nations Tuesday more isolated in the world body than every before.

For years, any U.N. debate, including those on women's rights or postage stamps, has included denunciations of Israel by Arab nations and their supporters, but Israel now finds itself with fewer friends to stand up against the anti-Israel majority, according to a number of Western diplomats.

Even the United States and Canada, which with Costa Rica are the only nations always voting with Israel, have made public their concern about Israel's military activities in southern Lebanon and its construction of settlements on Arab land captured in the 1967 Six-Day war.

On some crucial issues, such as the 1975 anti-Israeli resolution equating Zionism with racism, the Western European nations and some Latin American and African countries voted with Israel or abstained. But these nations do not stand up for Israel when it is condemned these days -- as it frequently is -- for Lebanon or the settlements question, the two issues diplomats say have deepened Israel's isolation.

Israel's response to criticism here has been to stand on its head Groucho Marx's famous dictum that he would not want to belong to any club that would have him for a member.

Israeli Ambassador Yehuda Blum and his aides have attacked the United Nations, saying in effect that any organization that condemns Israel does not deserve to be respected.

"I would prefer to have the majority behind me," Blum said in an interview, "but the decisive criterion for us has to be whether we believe we are right in what we are doing.

"Our isolation is the latter-day translation of the Jewish condition." he said. Lebanon and the settlements, he said, could be replaced by other issues. "No matter what we do we would come in for this kind of criticism."

One diplomat here said, however, that "Lebanon and the settlements have made it easier for nations to vote against Israel -- less afraid of being called anti-Semitic." Guilt over the Holocaust is ebbing, he added, citing the West German Decision to send its foreign minister to meet with Palestine Liberation Organization leader Yasser Arafat.

An ambassador whose country usually supports Israel criticized Israeli public relations tactics. "If they are trying to make it easier on their friends here, they are not very smart," he added.

Many of Israel's friends agree.

"Israel has drifted into a policy in Lebanon that no one can defend," another diplomat said. "It's running a quisling movement in another country and running it with arms."

A U.N. force composed of troops from Ireland, Norway, the Netherlands, France, Fiji, Nepal, Nigeria and Senegal is stationed in southern Lebanon and has been frustrated -- and shot at -- by the Lebanese Christian forces of Maj. Saad Haddad, which are armed by and allied with Israel.

On his last day in the Security Council chamber, Andrew Young said the strength of Israel in its early days "was that it was based on a moral foundation and yet Israel now is rapidly spending its moral capital, wasting it in pursuit of violence and destruction in Lebanon" and in the building of settlements.

"What he called moral capital was in a certain sense a guilt complex," Blum commented. The Begin government finds its critics -- including its Israeli critics -- wrong.

A new generation has grown up for whom the origin of the Middle East problem was the Six-Day War, Blum said. That means that Israel is an occupying power."Those of us with longer memories know better," Blum said.

A supporter of Israel who thinks Israel's course is dangerous for the Jewish state's future spoke in almost the same terms but with a different message.

The new generation he described included Palestinians who grew up in refugee camps and watched U.N. Resolutions fail to do anything to improve the Palestinians' lot. Now their determination to affect change coincides with changing perceptions in the world.

Israelis have a quick explanation for the world's change -- oil.

"I wouldn't want to equate one's moral capital with oil." Blum said of nations that have distanced themselves from Israel in recent years. "All the criticism fits into the pattern of forming better relationships with the Arabs."

Blum went on the offensive against the United Nations last week with an article in The New York Times declaring the world body is in a steady decline because it is dominated "by an unholy alliance of dictatorships and totalitarian regimes."

When the anti-Israel resolutions begin to pour forth at the General Assembly, Blum will be firing back. The Jewish people have always been called names, Blum said. "The great change in the Jewish people's status is that when people call us names now I can get up and exercise my right of reply," he said with a smile.

Israel's siege mentality, created by the history of the Jews and the belligerence of Israel's neighbors, is evident at the United Nations.

If Lewis Carroll were writing today, Chaim Herzog, Blum's predecessor, once observed, Alice would only have had to wear a Star of David in the U.N. building to hear people cry "Off with the head."

Herzog was Israel's representative in 1975 when the 22 Arab nations and their supporters won U.N. Approval of a resolution equating Zionism with racism.

"The Jewish people will not forget this scene nor this vote," Herzog said then. "We shall not forget those who voted to attack our religion and our faith. We shall never forget." There were 70 votes for the resolution, 29 against it, 27 abstentions and 16 nations absent.

Any lessening of Israel's isolation would be helpful, diplomats friendly to Israel believe. Andrew Young reportedly has been urging African nations to resume diplomatic relations with Israel, but the Israelis are not working hard to encourage new friendships.